The present invention relates to a method and system for control of a two part type transmission including an auxiliary gear transmission mechanism and a main gear transmission mechanism provided in series in a vehicle power train, and more particularly relates to such a transmission system method and control which minimize wear on transmission elements.
The present patent application has been at least partly prepared from material included in Japanese Patent Application Ser. No. Showa 60-139983, which was filed by an applicant the same as the assignee or entity owed duty of assignment of the present patent application, and the present application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claims and the drawings thereof.
There are various known types of two part type transmission including, in series in a vehicle power train, an auxiliary gear transmission mechanism and a main gear transmission mechanism; and typically the auxiliary gear transmission mechanism is a so called overdrive mechanism which is controllable to provide either a directly connected speed stage or a speed increasing overdrive speed stage between its power input shaft and its power output shaft, while the main gear transmission mechanism is controllable to provide either a directly connected speed stage or at least one speed reducing speed stage (and typically two such speed reducing speed stages) between its power input shaft and its power output shaft. And typically the auxiliary gear transmission mechanism is connected between the vehicle engine and the main gear transmission mechanism. Such a two part type transmission is, for example, disclosed in Japanese Patent Laying Open Publication No. 57-179460.
With such a two part type transmission, if the auxiliary gear transmission mechanism is switched between its directly connected speed stage and its speed increasing overdrive speed stage, not only when the main gear transmission mechanism is switched to its directly connected speed stage, but also when said main gear transmission mechanism is switched to one or more of its speed reduction speed stages, then a relatively large number of speed stages of the transmission as a whole may be provided. Such systems are disclosed, for example in Japanese Patent Applications Ser. Nos. 46-26604 (1965) and 59-176299 (1984), which were both applied for by an applicant who is also the applicant of the Japanese patent application of which the priority is being claimed for the present patent application, and none of which is it intended hereby to admit as prior art to the present patent application except to the extent otherwise required by applicable law.
A problem that has occurred with such a system is as follows. In the above outlined construction, during the condition when the auxiliary gear transmission mechanism is switched to its speed increasing overdrive speed stage, the rotational speed of the power input shaft of the main gear transmission mechanism is relatively high, so that, if said main gear transmission mechanism is at this time switched to one of its speed reduction speed stages, then there is relatively rapid rotation between mutually rotating elements such as gears and shafts and so on of said main gear transmission mechanism, and this can cause the rate of wear on said mutually rotating elements to be higher than desirable.